In many wireless communication systems, various elements can operate within different frequency bands. Accordingly, separate radiating elements are required for each band. To provide dedicated antennas for each element would require an unacceptably large number of antennas. It is thus desirable to provide a compact antenna within a single structure capable of servicing all required frequency bands.
Base station antennas for cellular communication systems generally employ array antennas to allow control of the radiation pattern. Due to the narrow band nature of arrays, it is desirable to provide an individual array for each frequency range. When antenna arrays are superposed in a single antenna structure, the radiating elements must be arranged within the physical geometrical limitations of each array while minimizing undesirable electrical interactions between the radiating elements.
In accordance with the above, dual band antennas have been developed. For example, U.S. Pat. No. 7,283,101 to Bisiules et al. entitled “Antenna Element, Feed Probe; Dielectric Spacer, Antenna and Method of Communicating With a Plurality of Devices” discloses a dual band module used in connection with an antenna array. U.S. Pat. No. 7,283,101 is hereby incorporated by reference.
It has been found that a dipole element is particularly suited to being used in combination with a ring because the dipole element has a relatively low area (as viewed in plan perpendicular to the ring), and extends out of the plane of the ring. These characteristics may reduce coupling between the elements.
FIG. 1 is an isometric view of a prior art dual band antenna 100. The antenna 100 provides a broadband operation with low inter-modulation. Further, the radiating elements have a relatively small footprint.
As seen in FIG. 1, a sheet aluminum tray can provide a planar reflector 101, and a pair of angled side walls 102. The reflector 101 can carry five dual band modules 103 and a printed circuit board (PCB) 104 on its rear face (not shown). Each dual band module 103 can include (1) a crossed dipole element (CDE) centered in a microstrip annular ring (MAR), and (2) an additional CDE.
The dual band antenna 100 shown of FIG. 1 is advantageous because the high band dipole can be placed inside of the low band ring element. This leads to a very compact package. However, this antenna configuration is only good for achieving an azimuth beam width of approximately 60-70 degrees. The antenna configuration shown in FIG. 1 is not applicable for achieving a 45 degree azimuth beam width.
Accordingly, antennas have been developed to achieve a 45 degree beam width. FIG. 2 is an isometric view of a prior art single band antenna 200. In the antenna 200 of FIG. 2, the low band elements are configured in two columns to achieve a 45 degree beam width. However, this configuration does not allow room for any high band elements. Accordingly, the azimuth side lobes achieved are high.
U.S. Pat. No. 6,924,776 to Le et al. entitled “Wideband Dual Polarized Base Station Antenna Offering Optimized Horizontal Beam Radiation Patterns and Variable Vertical Beam Tilt,” U.S. Pat. No. 7,358,922 to Le et al. entitled “Directed Dipole Antenna,” and U.S. Pat. No. 7,053,852 to Timofeev et al. entitled “Crossed Dipole Antenna Element” disclose examples of directed dipole designs. U.S. Pat. Nos. 6,924,776, 7,358,922, and 7,053,852 are hereby incorporated by reference. In known directed dipole designs, directors have been disposed above a single crossed dipole.
For example, FIG. 3 is a perspective view of a prior art radiator element. As seen in FIG. 3, four dipole directors 40 are disposed above a single radiating element 14.
In view of the above, there remains a continuing, ongoing need for a dual band antenna that achieves a 45 degree azimuth beam width. Preferably, such an antenna includes both high band and low band elements in a compact package.